Home buttons on youtube

[AC Question]

I recently purchased a LG G3 and I am still unfamiliar with the ways to modify the home buttons so i don't know how to disable this but when I open the YouTube ape and play a video even in full screen or landscape mode i still have the row of home, back, and multi task buttons i have tried to disable them but the YouTube app does not appear in the list of apps you can disable this feature on it use to not be like this but i must have done something
PLEASE HELP!!!!

 

[Xhanchi]

idk